Magnetic read/write system and magnetic recording medium

ABSTRACT

A novel magnetic read/write system, in which a fixed MR head serves to read magnetically recorded data from a magnetic recording medium as it operates at a relative speed of 2.0 to 5.0 m/s with respect to the magnetic recording medium comprising a non-magnetic support and a magnetic layer. A fatty acid ester represented by general formula (I):                    
     where R 1  is a hydrocarbon having 4 or less carbons, and R 2  is a straight-chain hydrocarbon having 12 or more carbons, exists between a read element of the MR head and the magnetic layer. This magnetic read/write system exhibits improved adherence to heads, running durability, and wear resistance of the tape in low temperature conditions as well as at room temperature.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of Ser. No. 10/075,459 dated Feb. 15,2002 now U.S. Pat. No. 6,607,824.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a magnetic read/write system that usesa fixed MR head to read magnetically recorded data from a magneticrecording medium, and to such a magnetic recording medium. Moreparticularly, the present invention relates to a magnetic read/writesystem that employs a fixed MR head to read magnetically recorded datafrom a magnetic recording medium, with improved running durability,adherence to a head, and wear resistance and to such a magneticrecording medium.

2. Description of the Related Art

As the recording density of magnetic recording media increases, frictionbetween a magnetic layer and components of a reading device duringrunning has posed a significant problem and there is an increasing needto improve running durability, adherence to a head, and wear resistanceof such recording media.

To meet such needs, techniques have been developed where a fatty acidester is added to a magnetic layer of a magnetic recording medium thatis mainly composed of ferromagnetic powder and binder resin (JapanesePatent Laid-Open Publication No. Sho 50-22603, Japanese Patent Laid-OpenPublication No. Sho 50-153905, Japanese Patent Laid-Open Publication No.Sho 53-149302, Japanese Pent Laid-Open Publication No. Sho 55-139637,Japanese Patent Publication No. Sho 39-28367, Japanese PatentPublication No. Sho 41-18065, and Japanese Patent Publication No. Sho47-12950).

These techniques, however, suffer a problem that many of the estercompounds that have straight-chain alkyls, which bring about theirrelatively high lubricating performance, have high melting points andthus form deposits on the surface of the magnetic layer at lowtemperatures. To cope with this, some techniques employ a fatty acidester having a saturated or unsaturated branched hydrocarbon group withhigh molecular weight as an additive to the magnetic layer (JapanesePatent Publication No. Sho 47-12950, Japanese Patent Laid-OpenPublication No. Sho 58-218038, Japanese Patent Laid-Open Publication No.Sho 60-205827, Japanese Patent Laid-Open Publication No. Sho 61-294637,and Japanese Patent Laid-Open Publication No. Sho 62-125529). Onetechnique involves adding to the magnetic layer a fatty acid esterhaving the following general formula:

where R¹¹ is a straight-chain saturated alkyl having 6 to 12 carbons,R¹² is a straight-chain saturated alkyl having 4 to 10 carbons, and R isa straight-chain or branched alkyl having 4 to 22 carbons (JapanesePatent No. 2559259).

One type of magnetic read/write system, which has recently been put topractical use and is intended for use in a computer back-up system,reads data stored in a magnetic recording medium using a fixed MR headthat operates at a relative speed of 2.0 to 5.0 m/s with respect to therecording medium. The system, known as the linear tape drive system,operates on the basis of linear scanning, in which a magnetic tape(which may be referred to simply as a tape, hereinafter) is moved alongits length with respect to the fixed MR head as the data is read alongthat direction. Unlike a helical scanning system, which employs a rotaryhead, the magnetic tape is moved at high speeds in this system. As aresult, the tape is vigorously rubbed against the head or guide rolls,causing the magnetic coating to come off the tape. For this reason, therole of the lubricant has become ever more significant to minimizedamage to the coating, and should the coating come off the tape, it isdesirable that the coating does not stick to the surrounding area of thehead gap.

No conventional fatty acid ester has ever achieved satisfactoryperformance when added to the magnetic layer in such a system. Forexample, fatty acid esters that have a saturated or unsaturated branchedhydrocarbon with high molecular weight are less than satisfactory interms of film strength and lubricating performance of the magnetic layerunder low temperature conditions.

Fatty acid esters used in a magnetic disk as described in JapanesePatent No. 2559259 are less likely to crystallize and remain in a liquidstate at relatively low temperatures, exhibiting lubricating property.These fatty acid esters do not readily evaporate from the surface of themagnetic layer at high temperatures, nor do they form deposits at lowtemperatures since fatty acid units and alcohol units present in themolecule have a limited number of carbons. Thus, the fatty acid estersare capable of providing high running durability under variousconditions. However, the lubricating performance of these fatty acidesters is not sufficient because of their high dynamic viscosity.Therefore, a high friction results when the fatty acid esters areapplied to the tape. This causes abrasion of the coating.

The present invention addresses the above-identified problems associatedwith the prior art.

Accordingly, it is an objective of the present invention to provide amagnetic read/write system that uses a fixed MR head to readmagnetically recorded data from a magnetic recording medium that hasimproved adherence to a head, running durability and wear resistanceunder low temperature conditions, as well as at room temperature, and toprovide such a magnetic recording medium. In particular, the presentinvention aims at provision of a magnetic read/write system that uses amagnetic tape exhibiting improved performances in terms of theabove-described adherence, running durability, and wear resistance whenused in a linear tape drive system, in which the fixed MR head readsmagnetically recorded data from a magnetic recording medium formed as atape (i.e., a magnetic tape), such as DLT4, while operating at arelative speed of 2.0 to 5.0 m/s with respect to the recording medium.It is also an objective of the present invention to provide such amagnetic tape.

SUMMARY OF THE INVENTION

In the course of their studies to find a solution to the above-describedproblems, the present inventors have found that the above-describedobjectives can be achieved by providing a non-magnetic layer thatcontains a specific fatty acid ester and a fatty acid between anon-magnetic support and the above-described magnetic layer andultimately completed the present invention.

In one aspect, the present invention provides a magnetic read/writesystem, in which a fixed MR head serves to read magnetically recordeddata from a magnetic recording medium as it operates at a relative speedof 2.0 to 5.0 m/s with respect to the magnetic recording mediumcomprising a non-magnetic support and a magnetic layer, wherein a fattyacid ester represented by general formula (I):

where R¹ is a hydrocarbon having 4 or less carbons, and R² is astraight-chain hydrocarbon having 12 or more carbons, exists between aread element of the MR head and the magnetic layer.

In another aspect, the present invention provides such a magneticrecording medium comprising:

a non-magnetic support;

a magnetic layer containing a ferromagnetic powder and a binder resin,the magnetic layer formed over the non-magnetic support and having a drythickness of 0.5 μm; and

a non-magnetic layer containing a non-magnetic powder and a binderresin, the non-magnetic layer interposed between the non-magneticsupport and the magnetic layer, the non-magnetic layer containing as alubricant a fatty acid ester represented by general formula (I):

where R¹ is a hydrocarbon having 4 or less carbons, and R² is astraight-chain hydrocarbon having 12 or more carbons, and a fatty acidhaving 12 or more carbons.

The fatty acid ester of the general formula (I) for use with the presentinvention, which is derived from fatty acids having a hydrocarbon branchat 2′-position, has a low solidification point and does not suffer asignificant decrease in the lubricity in low temperature conditions. Inaddition, this fatty acid ester has a shorter fatty acid side chain ascompared to the conventional fatty acid esters as represented by thegeneral formula (II) and thus exhibits low dynamic viscosity and shearviscosity even in low temperature conditions. Accordingly, by using thefatty acid ester, not only can the friction and the wear in the tape bereduced in a wide temperature range, but also the durability undervarious environments is improved. Furthermore, in terms of physicalproperties, the fatty acid ester exhibits less oiliness, the propertybeing characteristic of fatty acid esters. This is believed tocontribute to the improvements in the adherence to a head and stickinessof the tape. In the present invention, the fatty acid ester of thegeneral formula (I) is added only to the non-magnetic layer and isallowed to gradually migrate from the non-magnetic layer through themagnetic layer to the surface thereof. In this manner, high durabilityand wear-resistance can be achieved even when the tape is moved at arelative speed of 2.0 to 5.0 m/s with respect to the fixed MR head.These effects are not obtained if the fatty acid ester is added only tothe magnetic layer. The concurrent presence of the fatty acid with thenon-magnetic powder in the non-magnetic layer makes it possible for thefatty acid ester to migrate in the manner described above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described in detail with reference topreferred embodiments.

<Non-magnetic Support>

A non-magnetic support for use in a recording medium of the presentinvention is a sheet of film and is properly selected from conventionalresin films made of resin materials including, but not limited to,polyesters, polyamides, or aromatic polyamides, or resin films formed bylaminating these films. Such films, as well as its thickness and otherparameters, are known, and should not be limited to a particular one.

<Magnetic Layer>

Ferromagnetic powder contained in the magnetic layer of the magneticrecording medium of the present invention is a ferromagnetic metalpowder that has a needle-like shape and preferably has an average majoraxis length of 0.15 μm or less, more preferably from 0.05 to 0.10 μm. Ifthe powder has an average major axis length exceeding 0.15 μm, theelectromagnetic conversion characteristics (in particular, S/N and C/Ncharacteristics) required of magnetic recording media will becomeinsufficient.

Preferably, the ferromagnetic powder is contained in the magnetic layercomposition in an amount of 70 to 90% by weight. If the amount of theferromagnetic powder is excessively large, the amount of binder isreduced and, as a result, the surface smoothness of the recording mediumafter calendering worsens. Conversely, if the amount of theferromagnetic material is excessively small, high read output cannot beachieved.

Examples of the binder resin for use in the magnetic layer include, butare not limited to, conventional thermoplastic resins, thermosettingresins, radiation cure resins, and mixtures thereof.

Preferably, the binder resin is contained in the magnetic layer in anamount of 5 to 40 parts by weight, particularly 10 to 30 parts by weightwith respect to 100 parts by weight of the ferromagnetic powder. If theamount of the binder resin is too small, the strength of the magneticlayer is reduced and running durability may be lowered. On the otherhand, if the amount is too large, the amount of the ferromagnetic metalpowder is reduced, resulting in a reduced electromagnetic conversioncharacteristic.

When a thermosetting resin is used as the binder resin, various knownpolyisocyanates can be used to serve as a cross-linking agent forhardening the binder resin. The amount of the cross-linking agentcontained in the magnetic layer is preferably from 10 to 30 parts byweight with respect to 100 weight parts of the binder resin. Ifnecessary, abrasives, dispersing agents such as surface active agents,higher fatty acids and various other additives may be added to themagnetic layer.

A coating for forming the magnetic layer is prepared by adding anorganic solvent to the above-described components. The organic solventmay be one or more solvents properly selected from ketone solventsincluding methylethylketone (MEK), methylisobutylketone andcyclohexanone, and aromatic compound solvents including toluene. The useof other organic solvents is also contemplated. The amount of theorganic solvent to be added is preferably from about 100 to about 900parts by weight with respect to 100 parts by weight of the total amountof solid content (such as the ferromagnetic metal powder and variousinorganic particles) and the binder resin.

In the present invention, the magnetic layer has a thickness of 0.50 μmor less, preferably from 0.05 to 0.50 μm, and more preferably from 0.10to 0.25 μm. The magnetic layer that is too thick may increase theself-magnetization loss and thickness loss.

<Non-magnetic Layer>

The magnetic recording medium of the present invention includes anon-magnetic layer interposed between the above-described magnetic layerand the non-magnetic support. In this manner, the electromagneticconversion characteristic of the thin-layered magnetic layer is enhancedand reliability of the recording medium is further improved.

One characteristic of the present invention resides in that thenon-magnetic layer contains as a lubricant a fatty acid esterrepresented by the following general formula:

where R¹ is a hydrocarbon having 4 or less carbons, and R² is astraight-chain hydrocarbon having 12 or more carbons. Among such fattyacid esters, cetyl 2-ethylhexanoate, stearyl 2-ethylhexanoate, myristyl2-ethylhexanoate and stearyl 2-ethylbutanoate are preferred, with cetyl2-ethylhexanoate being particularly preferred.

By adding these fatty acid esters to the non-magnetic layer, the DLT4durability as well as adherence to head can further be improved ascompared to using conventional fatty acid esters. Also, the decrease inthe durability due to discharge, which is seen when fatty acid esterswith melting points of 30° C. or higher are used, does not take place inrelatively low temperature environments. Also, the fatty acid esters ofthe present invention, serving as a lubricant, have a smaller dynamicviscosity and a shear viscosity due to their relatively shorter carbonchains than those of the conventional fatty acid esters. Accordingly,damage to the coating caused by the friction between the magnetic layerof the magnetic tape and a back-coat layer is reduced. If the fatty acidester having the general formula (I) has R¹ containing 5 or more carbonsor has its ethyl replaced with an alkyl with 3 or more carbons, thefatty acid ester becomes oily, which affects the adherence to a head andstickiness of the tape. If R³ has less than 12 carbons, the fatty acidester tends to crystallize in low temperature conditions and tends toevaporate from the surface of the magnetic layer in high temperatureconditions.

Preferably, the lubricant is blended in the non-magnetic layer in anamount of 0.2 to 5 parts by weight with respect to 100 weight parts ofthe non-magnetic powder. If the amount is less than 0.2 parts by weight,the desired effects cannot be achieved. If the amount exceeds 5 parts byweight, improvements in the running durability or wear resistance of thetape are not as significant as expected from the amount. In addition, ifthe amount is excessive, significant problems arise especially withtapes, such as reduced durability due to discharge and the magneticlayer sticking to the back-coat layer.

The non-magnetic layer contains at least non-magnetic powder, binderresin, and fatty acid with 12 or more carbons and has a thickness ofpreferably 2.5 μm or less, more preferably from 0.1 to 2.3 μm. Thethickness larger than 2.5 μm does not improve performance of thenon-magnetic layer any further. On the contrary, too large a thicknesscan often result in non-uniformity in thickness in a coating layer. Notonly does this require stricter coating conditions but also may resultin a reduced surface smoothness.

Various inorganic powders can be used as the non-magnetic powder for usein the non-magnetic layer. For example, needle-shaped non-magneticpowders, such as needle-shaped non-magnetic iron oxide (α-Fe₂O₃), arepreferably used. Various other non-magnetic powders, including calciumcarbonate (CaCO₃), titanium oxide (TiO₂), barium sulfate (BaSO₄), andα-alumina (α-Al₂O₃), may preferably be blended. The non-magnetic layerpreferably contains a carbon black, example of which includes furnaceblack for rubber, thermal black for rubber, black for color andacetylene black.

The carbon black and the inorganic powder are preferably blended at aratio of 100:0 to 10:90 by weight. The proportion of the inorganicpowder greater than 90 may lead to a problem in terms of surfaceelectrical resistance.

As with the case of the magnetic layer, the binder resin may be aconventional thermoplastic resin, thermosetting resin, radiation cureresin and a mixture thereof, with the radiation cure resin beingparticularly preferred.

It is essential that the non-magnetic layer of the present inventionfurther contain as an additive a fatty acid with 12 or more carbons,preferably stearic acid. When necessary, it may further contain adispersing agent, such as a surface-active agent, and various otheradditives.

<Back-coat Layer>

A back-coat layer is optionally provided for the purposes of improvingrunning stability and preventing static electricity from building up inthe magnetic layer. The back-coat layer preferably contains from 30 to80% by weight of carbon black, which may be any of commonly used carbonblacks and may be the same as that used in the non-magnetic layer. Inaddition to the carbon black, the back-coat layer may optionally containnon-magnetic inorganic powders, such as the abrasives used in themagnetic layer, a dispersing agent such as a surface-active agent, alubricant such as higher fatty acid, fatty acid ester and silicone oil,and various other additives.

The back-coat layer has a thickness of 0.1 to 1.0 μm, preferably 0.2 to0.8 μm (after calendering). The thickness greater than 1.0 μm results inexcessive friction between the recording medium and the path that therecording medium follows and is rubbed against. This leads to reducedrunning stability. On the other hand, the thickness less than 0.1 μmresults in the back-coat layer being abraded as the recording medium ismoved.

The above-described magnetic recording medium of the present inventionhas improved adherence to a head, running durability, and wearresistance of the tape and thus is suitable for use with fixed MR headsunder low temperature conditions as well as at room temperature. In anMR head, resistance of a read sensor, which uses a magnetic material,changes when the read sensor is exposed to magnetic field, which allowsthe MR head to read external magnetic signals. Output of an MR head isnot affected by the relative speed of the head with respect to therecording medium, and for this reason, MR heads can achieve high outputwhen used to read magnetically recorded data recorded with a high trackrecording density. In order to achieve high resolution and high RFcharacteristic, a typical MR head has a construction in which amagnetoresistive film (MR film) is interposed between a pair of magneticshield film (Shielded MR head).

In a preferred magnetic read/write system, data is first recordedmagnetically on the magnetic recording medium of the present inventionand the data is then read using a fixed MR head operated at a relativespeed of 2.0 to 5.0 m/s. The fatty acid ester of general formula (I)added to the non-magnetic layer of the magnetic recording medium isallowed to exist between the read element of the MR head and themagnetic layer.

EXAMPLES

The present invention will now be described with reference to examples.

Example 1

<Coating 1 for forming non-magnetic layer> Needle-shaped α-Fe₂O₃ 70parts by weight (DPN-250BW manufactured by TODA KOGYO Co., Ltd.)(Average minor axis diameter = 28 nm, BET = 55 m²/g) Carbon black (#850Bmanufactured 30 parts by weight by MITSUBISHI CHEMICAL Co., Ltd.)(Average particle size = 16 nm, BET = 200 m²/g, DBP oil absorbance = 70ml/100 g) α-Al₂O₃ (HIT60A manufactured 5.5 parts by weight by SUMITOMOCHEMICAL Co., Ltd.) (Average particle size = 0.18 μm, BET = 12 m²/g)Electron beam-curable vinyl chloride copolymer 20 parts by weight(Degree of polymerization = 300, polar group: —OSO₃K = 1.5/molecule)Election beam-curable polyurethane resin 8 parts by weight (Mn = 25000,polar group: sodium hypophosphite = 1/molecule) MEK 120 parts by weightToluene 120 parts by weight Cyclohexanone 60 parts by weight

The above-listed components were mixed and kneaded and dispersed using asand grinder mill.

The following additives and solvents were then added to adjustviscosity. This completed the non-magnetic coating 1.

Cetyl 2-ethylhexanoate 2 parts by weight Stearic acid 1 parts by weightMEK 40 parts by weight Toluene 40 parts by weight Cyclohexanone 40 partsby weight <Magnetic coating 1> Fe-based metal magnetic powder 100 partsby weight (containing 10 atm % Co and 5 atm % Al with respect to Fe(=100)) (He = 144.6 kA/m, σs = 130 Am²/kg, BET 57 m²/g, average majoraxis length = 0.10 μm) Vinyl chloride copolymer 10 parts by weight(MR110 manufactured by ZEON Co., Ltd) (Degree of polymerizalion = 300,polar group: —OSO₃K = 1.5/molecule) SO₃Na-containing polyurethane resin7 parts by weight (Mn = 25000, polar group conc. = 1/molecule) α-Al₂O₃12 parts by weight (HIT82 manufactured by SUMITOMO CHEMICAL Co., Ltd.)(Average particle size = 0.12 μm, BET = 20 m²/g) Myristic acid 2 partsby weight MEK 90 parts by weight Toluene 90 parts by weightCyclohexanone 120 parts by weight

The above-listed components were mixed and kneaded and dispersed using asand grinder mill.

The following solvents were then added to adjust viscosity, completingthe magnetic coating 1.

MEK 110 parts by weight Toluene 110 parts by weight Cyclohexanone 160parts by weight <Coating for forming back-coat layer> Carbon black 80parts by weight (Conductex SC manufactured by COLUMBIAN CARBON Co.,Ltd., average patlicle size = 20 nm, BET = 220 m²/g) Carbon black 1parts by weight (Sevacarb MT manufactured by COLUMBIAN CARBON Co., Ltd,average particle size = 350 nm, BET = 8 m²/g) α-Fe₂O₃ 1 parts by weight(TF100 manufactured by TODA KOGYO Co., Ltd, average particle size 0.1μm) Vinyl chloride-vinyl acetate-vinyl 65 parts by weight alcoholcopolymer (Ratio by weight of monomers = 92:3:5, average degree ofpolymerization = 420) Polyesterpolyurethane resin 35 parts by weight(UR-8300 manufactured by TOYOBO Co., Ltd.) MEK 260 parts by weightToluene 260 parts by weight Cyclohexanone 260 parts by weight

The components above were mixed and kneaded and dispersed using a sandgrinder mill.

The following additives and solvents were then added to adjustviscosity. This completed the coating for forming the back-coat layer.

MEK 210 parts by weight Toluene 210 parts by weight Cyclohexanone 210parts by weight

<Preparation of Magnetic Tape>

The coating 1 for non-magnetic layer was applied onto one surface of abiaxially oriented, laminated PEN (polyethylene naphthalate) film havinga thickness of 6.2 μm. The coating was then dried and subjected tocalendering. Subsequently, an electron beam was irradiated (5 Mrad) ontothe film in nitrogen atmosphere to harden the coating. The coating 1 formagnetic layer was then applied on top of the non-magnetic layer,oriented, dried, and subjected to calendering. After calendering, themagnetic layer and the non-magnetic layer had thicknesses of 0.2 μm and1.8 μm, respectively. Subsequently, the coating for back-coat layer wasapplied to the opposite surface of the PEN film, dried, and subjected tocalendering. After calendering, the back-coat layer had a thickness of0.5 μm.

The film roll obtained in this manner was left for 24 hours at roomtemperature and was then hardened in an oven for 24 hours at 60° C. Theroll was then cut into ½ inch-wide tapes, which in turn were fitted in acassette to make a sample magnetic tape.

Example 2

A sample magnetic tape was fabricated in the same manner as in Example 1except that stearyl 2-ethylhexanoate was used in place of cetyl2-ethylhexanoate in the non-magnetic coating 1.

Example 3

A sample magnetic tape was fabricated in the same manner as in Example 1except that myristyl 2-ethylhexanoate was used in place of cetyl2-ethylhexanoate in the non-magnetic coating 1.

Example 4

A sample magnetic tape was fabricated in the same manner as in Example 1except that stearyl 2-ethylbutanoate was used in place of cetyl2-ethylhexanoate in the non-magnetic coating 1.

Comparative Example 1

A sample magnetic tape was fabricated in the same manner as in Example 1except that cetyl 2-ethyldecanoate was used in place of cetyl2-ethylhexanoate in the non-magnetic coating 1.

Comparative Example 2

A sample magnetic tape was fabricated in the same manner as in Example 1except that decyl 2-ethyldecanoate was used in place of cetyl2-ethylhexanoate in the non-magnetic coating 1.

Comparative Example 3

A sample magnetic tape was fabricated in the same manner as in Example 1except that t-butyl stearate was used in place of cetyl 2-ethylhexanoatein the non-magnetic coating 1.

Comparative Example 4

A sample magnetic tape was fabricated in the same manner as in Example 1except that isocetyl stearate was used in place of cetyl2-ethylhexanoate in the non-magnetic coating 1.

Comparative Example 5

A sample magnetic tape was fabricated in the same manner as in Example 1except that isobutyl stearate was used in place of cetyl2-ethylhexanoate in the non-magnetic coating 1.

Comparative Example 6

A sample magnetic tape was fabricated in the same manner as in Example 1except that sec-butyl stearate was used in place of cetyl2-ethylhexanoate in the non-magnetic coating 1.

Comparative Example 7

A sample magnetic tape was fabricated in the same manner as in Example 1except that stearic acid was not added to the non-magnetic coating 1.

Comparative Example 8

A sample magnetic tape was fabricated in the same manner as in Example 1except that cetyl 2-ethylhexanoate was not added to the non-magneticcoating 1 and two parts by weight of cetyl 2-ethylhexanoate were addedto the magnetic coating 1.

Each of the magnetic recording media obtained in Examples andComparative Examples were measured for the following properties.

(Running Durability)

Using a DLT-4000 drive manufactured by Quantum (relative speed betweenthe fixed MR head and the magnetic tape=2.4 m/s), each tape was testedfor the running durability by passing the tape 1,000,000 times over thefixed MR head to read/write data from/to part of the tape at roomtemperature (about 23° C., 50% RH) and at 10° C., 20% RH. The tape wasdetermined to be defective when the number of retry attempts of theread/write operation increased or when it was no longer possible toread/write from/to the tape before the number of the tape pass reached1,000,000 times.

(Degree of Coating Abrasion After the Layers Were Rubbed Against EachOther.)

Using a horizontal high-speed tensile tester, model no. HTB-Smanufactured by Island Industry, the magnetic layer and the back-coatlayer of the tape were repeatedly rubbed against one another and thelayers were observed for abrasion using an optical microscope.Measurements were taken at a temperature of 20° C. and humidity of 60%.For measurement, the tape was mounted on a first guide roll of theDLT-4000 drive with the back-coat layer facing outside and in contactwith the magnetic layer. The tape was passed 300 times over a distanceof 50 mm at a speed of 2000 mm/min with the applied load of 40 g and theholding angle of 90°. After the 300 passes, the magnetic layer and theback-coat layer were observed for the degree of abrasion. Ratings weregiven on a scale of A, B and C; where A=no abrasion, B=moderateabrasion, and C=considerable abrasion.

<Adherence to Head>

Using a DLT-4000 drive manufactured by Quantum, each sample tape was runfor 2400 cycles to read/write data both at room temperature (about 23°C., 50% RH) and at 10° C., 20% RH. Subsequently, adherence to the headwas observed using an optical microscope at ×100. Ratings were given ona scale of A, B and C; where A=no adhesion to the head, B=moderateadhesion to head, and C=adhesion to the entire surface of the head.

The results are shown in Tables 1 to 3 below.

TABLE 1 Fatty acid Number of Number of DLT4 running Adherence ester incarbons carbons in durability (passes) to head non-magnetic in R¹ in R²in Rm 10° C. Coating Rm 10° C. layer formula (I) formula (I) temp. 20%abrasion temp. 20% Ex.1 cetyl 4 16 1 million 1 million A A A2-ethylhexanoate Ex.2 stearyl 4 18 1 million 1 million A A B2-ethylhexanoate Ex.3 myristyl 4 12 1 million 1 million B A A2-ethylhexanoate Ex.4 stearyl 2 18 1 million 1 million B A A2-ethylbutanoate Comp.Ex.1 cetyl 8 16 Half a 300,000 C A B2-ethyldecanoate million Comp.Ex.2 decyl 4 10 ¾ million 400,000 B A A2-ethyldecanoate

TABLE 2 Fatty acid DLT4 running Adherence ester in durability (passes)to head non-mag- Rm 10° C. Coating Rm 10° C. netic layer temp. 20%abrasion temp. 20% Comp.Ex.3 t-butyl- 700.000 300,000 B B B steareateComp.Ex.4 isocetyl 350.000 200,000 B B C steareate Comp.Ex.5 isobutyl500,000 300,000 B A A steareate Comp.Ex.6 sec-butyl 500,000 400,000 B AA steareate

TABLE 3 DLT4 running Adherence Non-magnetic durability (passes) to headpowder in non- Rm 10° C. Coating Rm 10° C. magnetic layer temp. 20%abrasion temp. 20% Ex.1 DPN-250BW 1 1 A A A (α-iron oxide, millionmillion needle-shaped) Comp. DPN-250BW 450,000 100,000 C B B Ex.7(α-iron oxide, needle-shaped) Comp. DPN-250BW 200,000  50,000 C C C Ex.8(α-iron oxide, needle-shaped)

As has been described thus far, the present invention provides amagnetic recording medium that exhibits improved adherence to heads,running durability, and wear resistance of the tape in low temperatureconditions as well as at room temperature. The magnetic recording mediumof the present invention is suitable for use in the magnetic read/writesystem employing a fixed MR head.

While presently preferred embodiments of the present invention have beendescribed, it should be appreciated that various changes andmodifications may be made by those skilled in the art without departingfrom the scope of the invention as set forth in the appended claims.

What is claimed is:
 1. An magnetic recording medium comprising: a non-magnetic support; a magnetic layer containing a ferromagnetic powder and a binder resin, the magnetic layer formed over the non-magnetic support and having a dry thickness of 0.5 μm or less; and a non-magnetic layer containing a non-magnetic powder and a binder resin, the non-magnetic layer interposed between the non-magnetic support and the magnetic layer, the non-magnetic layer containing as a lubricant a fatty acid ester represented by general formula (I):

 where R¹ is a hydrocarbon having 4 or less carbons, and R² is a straight-chain hydrocarbon having 12 or more carbons, and a fatty acid having 12 or more carbons.
 2. The magnetic recording medium according to claim 1, wherein the non-magnetic support comprises at least one member selected from the group consisting of a polyester, polyamide and an aromatic polyamide.
 3. The magnetic recording medium according to claim 1, wherein the ferromagnetic powder is a ferromagnetic metal powder that has an average axis length of from 0.15 μm or less.
 4. The magnetic recording medium according to claim 1, wherein the ferromagnetic powder is present in an amount of from 70 to 90% by weight.
 5. The magnetic recording medium according to claim 1, wherein the resin binder contained in the magnetic layer is present in an amount of from 5 to 40 parts by weight with respect to the weight of the ferromagnetic powder.
 6. The magnetic recording medium according to claim 1, wherein the resin binder contained in the magnetic layer is present in an amount of from 10 to 30 parts by weight with respect to the weight of the ferromagnetic powder.
 7. The magnetic recording medium according to claim 1, wherein the resin binder contained in the non-magnetic layer is a radiation cure resin.
 8. The magnetic recording medium according to claim 1, wherein the magnetic layer has a thickness of from 0.05 to 0.50 μm.
 9. The magnetic recording medium according to claim 1, wherein the magnetic layer has a thickness of from 0.10 to 0.25 μm.
 10. The magnetic recording medium according to claim 1, wherein the fatty acid ester is at least one member selected from the group consisting of cetyl 2-ethylhexanoate, stearyl 2-ethylhexanoate, myristyl 2-ethylhexanoate and stearyl 2-ethylbutanoate.
 11. The magnetic recording medium according to claim 1, wherein the non-magnetic layer has a thickness of from 0.1 to 2.3 μm.
 12. The magnetic recording medium according to claim 1, wherein the non-magnetic powder is an inorganic powder.
 13. The magnetic recording medium according to claim 1, wherein the non-magnetic powder is a blend of calcium carbonate, titanium oxide, barium sulfate and α-alumina.
 14. The magnetic recording medium according to claim 1, wherein the fatty acid is stearic acid.
 15. A magnetic read/write system, in which a fixed MR head serves to read magnetically recorded data from a magnetic recording medium as it operates at a relative speed of 2.0 to 5.0 m/s with respect to the magnetic recording medium comprising a non-magnetic support and a magnetic layer, wherein a fatty acid ester represented by general formula (I):

where R¹ is a hydrocarbon having 4 or less carbons, and R² is a straight-chain hydrocarbon having 12 or more carbons, exists between a read element of the MR head and the magnetic layer, wherein the magnetic recording medium comprises a non-magnetic supports; a magnetic layer containing a ferromagnetic powder and a binder resin, the magnetic layer formed over the non-magnetic support and having a dry thickness of 0.5 μm or less; and a non-magnetic layer containing a non-magnetic powder and a binder resin, the non-magnetic layer interposed between the non-magnetic support and the magnetic layer, the non-magnetic layer containing as a lubricant said fatty acid ester and a fatty acid having 12 or more carbons. 